1. Field of the Invention
The instant invention is directed to a process for the synthesis of mixtures including aliphatic alcohols. More specifically, the instant invention is directed to a process for the synthesis of low boiling C.sub.1 to C.sub.9 aliphatic alcohol-containing mixtures from hydrogen and carbon monoxide.
2. Background of the Prior Art
The synthesis of methanol from carbon monoxide and hydrogen by the metal catalyzed Fischer-Tropsch process has long been known in the art. This process has enjoyed a revitalization what with the development of alcohol and so called gasohol fuels. A key reason for this new interest in the use of alcohol-gasoline fuel mixtures, in addition to the obvious conservation of liquid petroleum, is the fact that alcohol in alcohol-gasoline or gasohol fuels generally have more favorable anti-knock qualities than do gasolines. This tends to raise the octane number of gasohol mixtures compared to straight gasoline.
Recent studies of alcohol based fuels have indicated that even more satisfactory results are obtainable with the use of higher aliphatic alcohols alone or in admixture with methanol and higher aliphatic alcohols. The referred to studies indicate that when a mixture of methanol and C.sub.2 -C.sub.9 saturated alcohols is used as a blend with gasoline, such fuel is found superior to gasohol, that is, the combination of gasoline and methanol or gasoline with methanol and ethanol, fuels presently known in the art.
Among the advantages of fuels incorporating aliphatic alcohols is reduced elevation in fuel blend vapor pressure compared to the presently employed gasohol. Increase in the vapor pressure of fuel blends results in vapor lock problems. This volatility problem, inherent in the use of methanol, decreases the drivability of such a fuel blend. On the other hand, a mixture of higher alcohols have a lower vapor pressure than methanol with a resultant decrease in vapor lock and improved drivability.
A requirement of alcohol-gasoline blends is their homogeneity. The alcohol and the gasoline must not separate into separate phases. It has been found that methanol is less soluble in the average gasoline than is a mixture of higher alcohols.
Another physical property of alcohol-gasoline blends, water tolerance, relates also to the prevention of phase separation. A low water tolerance results in the formation of two phases, an upper gasoline-rich phase and a lower alcohol-rich phase. This separation, a function of the amount of water in the two phases, can have highly undesirable effects such as corrosion of automobile fuel system components, engine stall and the like. It has been found that of all aliphatic alcohols methanol has the lowest water tolerance. C.sub.2 -C.sub.9 mixtures, which act as co-solvents for methanol, significantly improve the water tolerance of methanol by as much as 500%.
The above remarks emphasize the potential for gasoline-alcohol fuel blends wherein the alcohol constituent is a combination of methanol and higher aliphatic alcohols. However, the synthesis processes of the prior art result in the formation of methanol only or alcohol blends in which methanol predominates. There has been little disclosure in the prior art of processes in which higher alcohols, i.e., C.sub.2 -C.sub.9, are produced in sufficient amount to provide the necessary volume of higher alcohols for use in alcohol-gasoline fuel blends.
Among the more recent disclosures directed to processes for synthesizing mixtures of methanol and higher alcohols is U.S. Pat. No. 4,122,110 issued to Sugier et al. This patent discloses the formation of such a blend of alcohol from synthesis gas. The process of the Sugier et al patent is catalyzed by a catalyst which comprises at least four essential elements, copper, cobalt, a third metal selected from chromium, iron, vanadium and manganese and at least one alkali metal, preferably lithium, sodium or potassium. In this process, it is preferred to add an organic complexant to a common solution of the copper, cobalt and a third metal catalyst which, the reference teaches, results in a catalyst of higher selectivity.
Another recent disclosure directed to the synthesis of mixtures of methanol and higher alcohols is U.K. Patent Application GB No. 2,083,469 A. In this application, a process is recited in which a synthesis gas, containing hydrogen and carbon monoxide, is reacted in the presence of a catalyst based on chromium, zinc and at least one alkali metal.
Yet another recent publication, German OLS No. 3005551 A1, discloses a catalyst for the synthesis of methanol and higher alcohol mixtures. Although the catalyst of the '551 disclosure is used in the present invention, there is no disclosure in the application of a process for producing a satisfactory methanol-higher alcohol product mixture.
Still another recent reference, UK Patent Application GB No. 2,087,749A, discloses the synthesis of hydrocarbons, e.g., methane or alcohols, e.g., methanol, from a CO--H.sub.2 gas reactant feed in which the gas phase reactants contact a fixed bed catalyst while diluted with an inert liquid phase material.